I wondered why when I searched a collection I was getting search results from books not in that collection. What I found out was that if my collection was based on books added to the +Plus these resources section, then the search worked fine, but if I was using a collection based on library Mytags, it didn't work right. I don't know if this was noted elsewhere, but it is definitely nice to know. Evidently the same is true for collections made with ratings, but I haven't tested this. See these threads also.
Searching Collection on iPad? - Logos Bible Software Forums
Collections on iPad - Logos Bible Software Forums